1. Field of the Invention
The present invention relates to a sigma-delta modulator, and more particularly, to a sigma-delta modulator and an output rate reduction method.
2. Description of the Prior Art
Efficiency of conventional class A or class B amplifiers is usually less than 60%, and thus large-sized thermal diffuser is necessarily disposed. Digital amplifiers are more generally utilized because digital amplifiers amplify signals by switching techniques with efficiency up to more than 90%. Therefore, the large-sized thermal diffuser is no longer needed and the digital amplifier can be made very small.
The conventional digital amplifiers mostly use Pulse Width Modulation (PWM) with carrier signals. Therefore, the output spectrum of the digital amplifier includes carrier frequencies and sidebands, and which cause electromagnetic interference (EMI). To suppress EMI, PWM can be replaced by a sigma-delta modulator as the output spectrum of the sigma-delta modulator is similar to white noise. However, the data output rate of the sigma-delta modulator is higher than that of PWM, and which causes more switch loss in the digital amplifier.